Communication of conditions at a primary storage controller to a host

ABSTRACT

A primary storage controller is maintained in a copy relationship with a secondary storage controller, wherein the primary and secondary storage controllers are coupled to a host that is configurable to use the secondary storage controller instead of the primary storage controller. The primary storage controller determines occurrence of at least one condition in the primary storage controller, wherein the at least one condition occurs prior to a failure of the host to perform an Input/Output (I/O) operation with respect to at least one storage volume of the primary storage controller. The primary storage controller communicates the occurrence of the at least one condition to the host, wherein in response to the communicating the host is configured to determine whether to use the secondary storage controller instead of the primary storage controller based on the occurrence of the at least one condition.

BACKGROUND

1. Field

The disclosure relates to a method, system, and article of manufacturefor the communication of conditions at a primary storage controller to ahost.

2. Background

A host may be coupled to a primary storage controller and a secondarystorage controller. Storage volumes in the primary storage controllermay be copied via synchronous peer to peer remote copy operations to thesecondary storage controller. The primary and secondary storagecontrollers may in such a situation be referred to as being in amirrored configuration.

The host may issue write requests to the primary storage controller, andthe primary storage controller may replicate the writes to the secondarystorage controller; the secondary storage controller may acknowledge thewrites to the primary storage controller, and the primary storagecontroller may then acknowledge the writes to the host.

In certain situations, the host may not be able to perform I/Ooperations with one or more storage volumes of the primary storagecontroller. The inability to perform I/O operations with one or morestorage volumes of the primary storage controller may be because of thefailure of the one or more storage volumes in the primary storagecontroller, or because of the failure of the primary storage controlleritself. In such situations, the host may be able to substitute usage ofthe primary storage controller with the secondary storage controller(i.e., use the secondary storage controller instead of primary storagecontroller), such that host applications may continue to execute.

If a host application was previously accessing the primary storagecontroller and received indications of I/O failures, then swapping ofthe primary storage controller by the secondary storage controller thatmaintains copies of the storage volumes of the primary storagecontroller allows the host application to continue execution. From thehost application perspective, the swapping is transparent, i.e., hostapplications do not have to be aware that a swapping took place.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, a system, a computer program product, in which aprimary storage controller is maintained in a copy relationship with asecondary storage controller, wherein the primary and secondary storagecontrollers are coupled to a host that is configurable to use thesecondary storage controller instead of the primary storage controller.The primary storage controller determines occurrence of at least onecondition in the primary storage controller, wherein the at least onecondition occurs prior to a failure of the host to perform anInput/Output (I/O) operation with respect to at least one storage volumeof the primary storage controller. The primary storage controllercommunicates the occurrence of the at least one condition to the host,wherein in response to the communicating the host is configured todetermine whether to use the secondary storage controller instead of theprimary storage controller based on the occurrence of the at least onecondition.

In certain embodiments, the occurrence of the at least one condition iscaused by a loss of storage redundancy in the primary storagecontroller.

In further embodiments, the occurrence of the at least one condition iscaused by a performance degradation in the primary storage controller.

In yet further embodiments, the occurrence of the at least one conditionis caused by errors exceeding a threshold in the primary storagecontroller.

In additional embodiments, the occurrence of the at least one conditionis caused by an acute error in the primary storage controller from whichrecovery is not possible in the primary storage controller.

In yet additional embodiments, the copy relationship is a synchronouspeer to peer remote copy relationship. The primary storage controller isnot configured to substitute usage of the primary storage controllerwith usage of the secondary storage controller, and the determining ofthe occurrence of the at least one condition and the communicating ofthe occurrence of the at least one condition to the host, are performedin response to the primary storage controller determining that the hosthas capability to substitute usage of the primary storage controllerwith usage of the secondary storage controller, wherein thecommunicating provides an indication that requests a remedial action toan operator.

In further embodiments, in response to a determination that a freeze hasto be performed during synchronous peer to peer remote copy operationsor to use the secondary storage controller instead of the primarystorage controller, a grouping is performed at predetermined intervalsof time of a plurality of interrupts into a single interrupt to reduce atotal number of interrupts.

In still further embodiments, the primary storage controller receives arequest from the host for additional information regarding theoccurrence of at least one condition, in response to the communicating,by the primary storage controller, of the occurrence of the at least onecondition to the host. The primary storage controller sends therequested additional information, to the host, wherein in response tothe host receiving the additional information, the host determineswhether to use the secondary storage controller instead of the primarystorage controller.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a computing environment thatincludes one or more hosts coupled to at least one primary storagecontroller and at least one secondary storage controller that are in asynchronous copy relationship, in accordance with certain embodiments;

FIG. 2 illustrates a first flowchart that shows at least how the primarystorage controller communicates the occurrence of at least one conditionin the primary storage controller to the host, in accordance withcertain embodiments;

FIG. 3 illustrates a second flowchart that shows operations performed bythe host and the primary storage controller, in accordance with certainembodiments;

FIG. 4 illustrates a third flowchart that shows grouping of interruptsat predetermined intervals of time, in accordance with certainembodiments; and

FIG. 5 illustrates a block diagram of a computational system that showscertain elements that may be included in at least the primary storagecontroller or host of FIG. 1, in accordance with certain embodiments.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments. It is understood that other embodiments may be utilized andstructural and operational changes may be made.

Communications and Recovery in Storage Systems

Storage controllers are designed for continuous availability. However,there are some recovery scenarios that may take several seconds and thatmay impact host I/O. If the storage controller is not in a mirroredconfiguration with host software that is configurable to swap to analternate storage controller, then it is appropriate for the storagecontroller to do all it can to recover from errors, even if the recoveryperiod is long and impacts production.

However, if the storage controller is in a mirrored configuration withhost software that is configurable to swap to an alternate storagecontroller, then it may improve availability if a swap to the alternatestorage controller were to occur instead of continuing to try andrecover from the failing storage controller. In addition, the quickerthe swap can occur, the higher the availability of the storage system.

Certain embodiments allow a primary storage controller in a mirroredconfiguration with a secondary storage controller, when supported via ahost having capabilities to swap storage controllers, to sendcommunications to the host of any recovery processing that will impacthost I/Os for an extended period. In such a situation, the host mayinitiate swapping of the primary storage controller with the secondarystorage controller. This may allow the former primary storage controllerto complete its recovery while allowing host I/Os to proceed by usingthe former secondary storage controller.

In certain embodiments the primary storage controller presents existingnotifications of remote copy suspension events in a more consolidatedform by grouping multiple interrupts into a single interrupt.

Certain embodiments may reduce the overhead of lengthy error recovery,improve scalability, and cause faster freezing and swapping of storagecontrollers.

Exemplary Embodiments

FIG. 1 illustrates a block diagram of a computing environment 100 thatincludes one or more hosts 102 coupled to at least one primary storagecontroller 104 and at least one secondary storage controller 106 thatare in a synchronous copy relationship, in accordance with certainembodiments.

The primary storage controller 104, the secondary storage controller106, and the host 102 may comprise any suitable computational deviceincluding those presently known in the art, such as, a personalcomputer, a workstation, a server, a mainframe, a hand held computer, apalm top computer, a telephony device, a network appliance, a bladecomputer, a server, etc.

The primary storage controller 104 and secondary storage controller 106may each include or be coupled to groupings of any suitable storagedevices, such as, hard disks, solid state disks, linear storage devices,etc. In certain embodiments, the physical storage present in storagedevices controlled via the primary storage controller 104 and thesecondary storage controller 106 may be logically addressed as storagevolumes 110 a . . . 110 m, 112 a . . . 112 n as shown in FIG. 1.

The primary storage controller 104, the secondary storage controller106, and the host 102 may communicate over a network (not shown), wherethe network may comprise any suitable network, such as, the Internet, astorage area network, a wide area network, a local area network, etc. Incertain embodiments, the primary storage controller 104, the secondarystorage controller 106, and the host 102 may be implemented in a cloudcomputing environment and may provide processing and storage services tousers.

The primary storage controller 104 may allow the performing of peer topeer remote copy operations 114 between the primary storage controller104 and the secondary storage controller 106. In certain embodiments,the primary storage controller 104 and the secondary storage controller106 may be separated by distances of over ten kilometers or more. Forexample, in certain embodiments the primary storage controller 104 andthe secondary storage controller 106 may be separated by distances ofover hundred kilometers. In certain embodiments, the peer to peer remotecopy operations 114 may be performed synchronously to ensure that thesame data is maintained in the primary storage controller 104 and thesecondary storage controller 106.

The primary storage controller 104 includes a potential error surfacingapplication 116 that can send communications to the host 102 indicatingthat certain conditions have occurred in the primary storage controller104 that may potentially result in a failure or a reduced performance ata future point in time. At the time the potential error surfacingapplication 116 sends the communications to the host 102, the userapplication 118 on the host 102 can still perform I/O or is waiting toperform I/O with respect to the storage volumes 110 a . . . 110 m of theprimary storage controller 104.

The host 102 includes a storage controller usage replacement managementapplication 120 that is capable of swapping the primary storagecontroller 104 with the secondary storage controller 106. Since thestorage controller usage replacement management application 120 iscapable of replacing usage of the primary storage controller 104 withthe secondary storage controller 106, it is preferable to perform thereplacement in usage, in case the primary storage controller 104indicates to the host 102 that the performance has been impactedconsiderably, or that potential failures are likely, or that errorrecovery is anticipated to take a considerable period of time. The aboveis not an exhaustive list of conditions under which the storagecontroller usage replacement management application 120 swaps theprimary storage controller 104 for the secondary storage controller 106,wherein swapping or replacing usage of the primary storage controller104 for the secondary storage controller 106 means that the secondarystorage controller 106 is used instead of the primary storage controller104. It should be noted that there is no physical replacement of theprimary storage controller 104 with the secondary storage controller106.

Therefore, FIG. 1 shows certain embodiments in which in response tocertain indications that provide a warning or a possibility of potentialerror from the primary storage controller 104 to the host 102, the host102 may swap the primary storage controller 104 for the secondarystorage controller 106. As a result, the performance of user application118 is not impaired by a failure of I/O operations to a defectiveprimary storage controller. While in FIG. 1, one primary storagecontroller is shown in a copy relationship with one secondary storagecontroller, in alternative embodiments other pairs of primary andsecondary storage controllers in a copy relationship may also bemaintained within the computing environment 100.

FIG. 2 illustrates a first flowchart 200 that shows at least how theprimary storage controller 104 communicates the occurrence of at leastone condition in the primary storage controller 104 to the host 102, inaccordance with certain embodiments. The operations shown in FIG. 2 maybe implemented at least by the potential error surfacing application 116that executes in the primary storage controller 104.

Control starts at block 202, in which a primary storage controller 104is maintained in a copy relationship with a secondary storage controller106, wherein the primary storage controller 104 and the secondarystorage controller 106 are coupled to a host 102 that is configurable touse the secondary storage controller 106 instead of the primary storagecontroller 104 via a storage controller usage replacement managementapplication 120.

The primary storage controller 104 determines (at block 204) that thehost 102 has capability to substitute usage of the primary storagecontroller 104 with usage of the secondary storage controller 106. Thenthe primary storage controller 104 determines (at block 206) occurrenceof at least one condition in the primary storage controller 104, whereinthe at least one condition occurs prior to a failure of the host 102 toperform an Input/Output (I/O) operation with respect to at least onestorage volume of the primary storage controller 104, wherein theoccurrence of the at least one condition is caused by:

-   (1) A loss of storage redundancy in the primary storage controller    (e.g., via a failure of a Redundant Array of Independent Disk (RAID)    in a RAID configuration on the primary storage controller 104, where    there is no likelihood of I/O error as a result of the failure of    the disk because of the redundancy of RAID);-   (2) a performance degradation in the primary storage controller    (e.g., performance has fallen below a predetermined or preconfigured    level of performance);-   (3) errors exceeding a threshold in the primary storage controller;    or-   (4) an acute error in the primary storage controller from which    recovery is not possible in the primary storage controller.

From block 206, control proceeds to block 208 in which the primarystorage controller 104 communicates the occurrence of the at least onecondition to the host 102, wherein in response to the communicating thehost 102 is configured to determine whether to use the secondary storagecontroller 106 instead of the primary storage controller 104 based onthe occurrence of the at least one condition. In certain situations, thehost 102 may find it preferable not to replace usage of the primarystorage controller 104 with usage of the secondary storage controller106.

Therefore, FIG. 2 illustrates certain embodiments in which the primarystorage controller 104 sends communications on the occurrence of certainconditions to the host 102, and the host 102 may then analyze theconditions after optionally seeking additional information to determinewhether or not to use the secondary storage controller 106 instead ofthe primary storage controller 104.

FIG. 3 illustrates a second flowchart 300 that shows operationsperformed by the host 102 and the primary storage controller 104, inaccordance with certain embodiments. The host operations 306 are shownto the left of the dashed line 304 and the primary storage controlleroperations 308 are shown to the right of the line 304.

Control starts at block 310, in which the host 102 receivescommunication from the primary storage controller 104 of the occurrenceof the at least one condition. It may be noted that the sending ofcommunication from the primary storage controller 104 to the host 102was shown in block 208 of FIG. 2.

In certain embodiments, the host 102 may request (at block 312)additional information from the primary storage controller 104 regardingthe occurrence of the at least one condition. The additional informationrequested may be different for different conditions.

The primary storage controller 104 receives (at block 314) the requestfrom the host 102 for additional information regarding the occurrence ofthe at least one condition. The primary storage controller 104 sends (atblock 316) the requested additional information, to the host 102. Theadditional information may provide detailed status of various flags,registers, state of certain variables, etc.

Control proceeds to block 318, in which the host 102, in response toreceiving the additional information, determines whether to use thesecondary storage controller 106 instead of the primary storagecontroller 104. The determination of whether to replace the usage of theprimary storage controller 104 with the usage of the secondary storagecontroller 106 may be based on an assessment of the storage controllerusage replacement management application 120 on which option is likelyto improve system performance and provide faster responses to the userapplication 118.

FIG. 4 illustrates a third flowchart 400 that shows grouping ofinterrupts at predetermined intervals of time, in accordance withcertain embodiments.

In certain embodiments, there may be numerous (e.g., over a thousand)storage volume pairs in a copy relationship between the primary storagecontroller 104 and the secondary storage controller 106. The overhead ofmanaging the environment on a volume by volume (or volume pair by volumepair) basis may be prohibitive, in terms of system resources andperformance. Certain embodiments may manage the environment in a moreefficient manner by grouping multiple interrupts generated by thefreezing of a large number of storage volumes, by grouping multipleinterrupts into a single interrupt at predetermined intervals of time,as shown in FIG. 4.

A freeze (i.e., a quiescence), of a storage volume is a state in whichno I/O operations are allowed to be performed on the storage volume.When a volume is frozen an interrupt is to be generated. However, with alarge number of volumes that may need to be frozen the interrupts mayoverwhelm the processing capabilities of the system or there may be asignificant amount of system overhead. In certain embodiments,interrupts of a group of volumes may be grouped together to generate asingle interrupt for the group.

Control starts at block 402, and from block 402, control may proceed toblock 404 and 406 in parallel. At block 404, a determination is made asto whether the freeze is to be performed during synchronous peer to peerremote copy operations (the freeze referred to in block 404 may beinitiated in response to a peer to peer remote copy suspension event).If so, control proceeds to block 410 in which at predetermined intervalsof time a plurality of interrupts corresponding to the freeze aregrouped into a single interrupt to reduce a total number of interrupts,and the process stops (at block 412). If not, control proceeds to block412 where the process stops.

At block 406, a determination is made as to whether the freeze to beperformed to replace usage of the primary storage controller 104 withthe secondary storage controller 106 (the freeze referred to in block406 may be necessitated because a swap of the primary storage controller104 with the secondary storage controller 106 is initiated as a resultof a failure, such as a disk failure event, in the primary storagecontroller 104). If so, control proceeds to block 410 in which atpredetermined intervals of time a plurality of interrupts correspondingto the freeze are grouped into a single interrupt to reduce a totalnumber of interrupts, and the process stops (at block 412). If not,control proceeds to block 412 where the process stops.

Therefore, FIG. 4 illustrates certain embodiments in which interruptsthat may be generated in a predetermined interval of time are groupedinto fewer interrupts to improve system performance. For example, allinterrupts generated every five seconds may be grouped and a groupinterrupt may be issued every five seconds.

FIGS. 1-4 illustrate certain embodiments in which a primary storagecontroller that is aware of the primary and secondary storage controllerswapping capabilities of the host may warn the host of impendingproblems, so as to allow the host an opportunity to determine whether itis more effective to swap the primary and the secondary storagecontrollers or whether to wait for the primary storage controller tocomplete error recovery. In certain embodiments, to improve the system,instead of generating an interrupt corresponding to each volume orvolume-pair during freezing of each volume, a plurality of potentialinterrupts are grouped together at predetermined intervals of time togenerate a single interrupt.

Additional Embodiment Details

The described operations may be implemented as a method, apparatus orcomputer program product using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. Accordingly, aspects of the embodiments may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,aspects of the embodiments may take the form of a computer programproduct embodied in one or more computer readable medium(s) havingcomputer readable program code embodied there.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java*, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider). *Java is a trademark or registered trademark of Oracle and/orits affiliates.

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

FIG. 5 illustrates a block diagram that shows certain elements that maybe included in the primary storage controller 104. the secondary storagecontroller 106, and the host 102, in accordance with certainembodiments. The system 500 may comprise the primary storage controller104, the secondary storage controller 106, and the host 102, and mayinclude a circuitry 502 that may in certain embodiments include at leasta processor 504. The system 500 may also include a memory 506 (e.g., avolatile memory device), and storage 508. The storage 508 may include anon-volatile memory device (e.g., EEPROM, ROM, PROM, RAM, DRAM, SRAM,flash, firmware, programmable logic, etc.), magnetic disk drive, opticaldisk drive, tape drive, etc. The storage 508 may comprise an internalstorage device, an attached storage device and/or a network accessiblestorage device. The system 500 may include a program logic 510 includingcode 512 that may be loaded into the memory 506 and executed by theprocessor 504 or circuitry 502. In certain embodiments, the programlogic 510 including code 512 may be stored in the storage 508. Incertain other embodiments, the program logic 510 may be implemented inthe circuitry 502. Therefore, while FIG. 5 shows the program logic 510separately from the other elements, the program logic 510 may beimplemented in the memory 506 and/or the circuitry 502.

Certain embodiments may be directed to a method for deploying computinginstruction by a person or automated processing integratingcomputer-readable code into a computing system, wherein the code incombination with the computing system is enabled to perform theoperations of the described embodiments.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

Further, although process steps, method steps, algorithms or the likemay be described in a sequential order, such processes, methods andalgorithms may be configured to work in alternate orders. In otherwords, any sequence or order of steps that may be described does notnecessarily indicate a requirement that the steps be performed in thatorder. The steps of processes described herein may be performed in anyorder practical. Further, some steps may be performed simultaneously.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

At least certain operations that may have been illustrated in thefigures show certain events occurring in a certain order. In alternativeembodiments, certain operations may be performed in a different order,modified or removed. Moreover, steps may be added to the above describedlogic and still conform to the described embodiments. Further,operations described herein may occur sequentially or certain operationsmay be processed in parallel. Yet further, operations may be performedby a single processing unit or by distributed processing units.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended.

What is claimed is:
 1. A method, comprising: maintaining a primarystorage controller in a copy relationship with a secondary storagecontroller, wherein the primary and secondary storage controllers arecoupled to a host that is configurable to use the secondary storagecontroller instead of the primary storage controller; determining, bythe primary storage controller, occurrence of at least one condition inthe primary storage controller, wherein the at least one conditionoccurs prior to a failure of the host to perform an Input/Output (I/O)operation with respect to at least one storage volume of the primarystorage controller; and communicating, by the primary storagecontroller, the occurrence of the at least one condition to the host,wherein in response to the communicating the host is configured todetermine whether to use the secondary storage controller instead of theprimary storage controller based on the occurrence of the at least onecondition.
 2. The method of claim 1, wherein the occurrence of the atleast one condition is caused by a loss of storage redundancy in theprimary storage controller.
 3. The method of claim 1, wherein theoccurrence of the at least one condition is caused by a performancedegradation in the primary storage controller.
 4. The method of claim 1,wherein the occurrence of the at least one condition is caused by errorsexceeding a threshold in the primary storage controller.
 5. The methodof claim 1, wherein the occurrence of the at least one condition iscaused by an acute error in the primary storage controller from whichrecovery is not possible in the primary storage controller.
 6. Themethod of claim 1, wherein: the copy relationship is a synchronous peerto peer remote copy relationship; the primary storage controller is notconfigured to substitute usage of the primary storage controller withusage of the secondary storage controller; and the determining of theoccurrence of the at least one condition and the communicating of theoccurrence of the at least one condition to the host, are performed inresponse to the primary storage controller determining that the host hascapability to substitute usage of the primary storage controller withusage of the secondary storage controller, wherein the communicatingprovides an indication that requests a remedial action to an operator.7. The method of claim 6, the method further comprising: in response todetermining that a freeze has to be performed during synchronous peer topeer remote copy operations or to use the secondary storage controllerinstead of the primary storage controller, grouping at predeterminedintervals of time a plurality of interrupts into a single interrupt toreduce a total number of interrupts.
 8. The method of claim 1, themethod further comprising: receiving, by the primary storage controller,a request from the host for additional information regarding theoccurrence of the at least one condition, in response to thecommunicating, by the primary storage controller, of the occurrence ofthe at least one condition to the host; and sending, by the primarystorage controller, the requested additional information, to the host,wherein in response to the host receiving the additional information,the host determines whether to use the secondary storage controllerinstead of the primary storage controller.
 9. A system, comprising: amemory; and a processor coupled to the memory, wherein the processorperforms operations, the operations comprising: maintaining a primarystorage controller in a copy relationship with a secondary storagecontroller, wherein the primary and secondary storage controllers arecoupled to a host that is configurable to use the secondary storagecontroller instead of the primary storage controller; determining, bythe primary storage controller, occurrence of at least one condition inthe primary storage controller, wherein the at least one conditionoccurs prior to a failure of the host to perform an Input/Output (I/O)operation with respect to at least one storage volume of the primarystorage controller; and communicating, by the primary storagecontroller, the occurrence of the at least one condition to the host,wherein in response to the communicating the host is configured todetermine whether to use the secondary storage controller instead of theprimary storage controller based on the occurrence of the at least onecondition.
 10. The system of claim 9, wherein: the occurrence of the atleast one condition is caused by a loss of storage redundancy in theprimary storage controller; and the occurrence of the at least onecondition is caused by a performance degradation in the primary storagecontroller.
 11. The system of claim 9, wherein: the occurrence of the atleast one condition is caused by errors exceeding a threshold in theprimary storage controller; and the occurrence of the at least onecondition is caused by an acute error in the primary storage controllerfrom which recovery is not possible in the primary storage controller.12. The system of claim 9, wherein: the copy relationship is asynchronous peer to peer remote copy relationship; the primary storagecontroller is not configured to substitute usage of the primary storagecontroller with usage of the secondary storage controller; and thedetermining of the occurrence of the at least one condition and thecommunicating of the occurrence of the at least one condition to thehost, are performed in response to the primary storage controllerdetermining that the host has capability to substitute usage of theprimary storage controller with usage of the secondary storagecontroller, wherein the communicating provides an indication thatrequests a remedial action to an operator.
 13. The system of claim 12,the operations further comprising: in response to determining that afreeze has to be performed during synchronous peer to peer remote copyoperations or to use the secondary storage controller instead of theprimary storage controller, grouping at predetermined intervals of timea plurality of interrupts into a single interrupt to reduce a totalnumber of interrupts.
 14. The system of claim 9, the operations furthercomprising: receiving, by the primary storage controller, a request fromthe host for additional information regarding the occurrence of the atleast one condition, in response to the communicating, by the primarystorage controller, of the occurrence of the at least one condition tothe host; and sending, by the primary storage controller, the requestedadditional information, to the host, wherein in response to the hostreceiving the additional information, the host determines whether to usethe secondary storage controller instead of the primary storagecontroller.
 15. A computer program product, the computer program productcomprising a computer readable storage medium having computer readableprogram code embodied therewith, the computer readable program codeconfigured to perform operations, the operations comprising: maintaininga primary storage controller in a copy relationship with a secondarystorage controller, wherein the primary and secondary storagecontrollers are coupled to a host that is configurable to use thesecondary storage controller instead of the primary storage controller;determining, by the primary storage controller, occurrence of at leastone condition in the primary storage controller, wherein the at leastone condition occurs prior to a failure of the host to perform anInput/Output (I/O) operation with respect to at least one storage volumeof the primary storage controller; and communicating, by the primarystorage controller, the occurrence of the at least one condition to thehost, wherein in response to the communicating the host is configured todetermine whether to use the secondary storage controller instead of theprimary storage controller based on the occurrence of the at least onecondition.
 16. The computer program product of claim 15, wherein: theoccurrence of the at least one condition is caused by a loss of storageredundancy in the primary storage controller; and the occurrence of theat least one condition is caused by a performance degradation in theprimary storage controller.
 17. The computer program product of claim15, wherein: the occurrence of the at least one condition is caused byerrors exceeding a threshold in the primary storage controller; and theoccurrence of the at least one condition is caused by an acute error inthe primary storage controller from which recovery is not possible inthe primary storage controller.
 18. The computer program product ofclaim 15, wherein: the copy relationship is a synchronous peer to peerremote copy relationship; the primary storage controller is notconfigured to substitute usage of the primary storage controller withusage of the secondary storage controller; and the determining of theoccurrence of the at least one condition and the communicating of theoccurrence of the at least one condition to the host, are performed inresponse to the primary storage controller determining that the host hascapability to substitute usage of the primary storage controller withusage of the secondary storage controller, wherein the communicatingprovides an indication that requests a remedial action to an operator.19. The computer program product of claim 18, the operations furthercomprising: in response to determining that a freeze has to be performedduring synchronous peer to peer remote copy operations or to use thesecondary storage controller instead of the primary storage controller,grouping at predetermined intervals of time a plurality of interruptsinto a single interrupt to reduce a total number of interrupts.
 20. Thecomputer program product of claim 15, the operations further comprising:receiving, by the primary storage controller, a request from the hostfor additional information regarding the occurrence of the at least onecondition, in response to the communicating, by the primary storagecontroller, of the occurrence of the at least one condition to the host;and sending, by the primary storage controller, the requested additionalinformation, to the host, wherein in response to the host receiving theadditional information, the host determines whether to use the secondarystorage controller instead of the primary storage controller.